1. Field
The subject invention is in the field of extendable/retractable apparatus such as tent poles, fishing rods and boat hooks which can be set at any length within a length range. More specifically it is in the field of such apparatus which incorporates mechanism by which one mechanism at one end of the apparatus operates and controls another mechanism at the other end of the apparatus. Still more specifically it is in the field of such apparatus and related mechanisms adapted for use with apparatus used in construction of dry walls in buildings, apparatus known in the trade as a flat finishing box, used in the crowning and finishing of taped joints between drywall panels.
2. Prior Art
Known prior art is shown in the patents listed below. These patents are:
U.S. Pat. No. 2,934,937
U.S. Pat. No. 3,105,262
U.S. Pat. No. 3,146,481
U.S. Pat. No. 3,090,984
U.S. Pat. No. 4,592,797
U.S. Pat. No. 5,088,147
U.S. Pat. No. 5,099,539
In the field of drywall construction and finishing, apparatus termed a flat finishing box is attached to a handle to enable the operator to apply the box to the joints being serviced by the box. To adapt the apparatus to various use situations various lengths of handles are needed to work with, for example, a variety of heights of ceilings and, also, the box must be set in a range of angles with respect to the long axis of the handle. The conventional apparatus comprises a fixed length handle with a lever at one end operable to lock the box pivoted at the other end of the handle at a specific angle to the handle axis. When a variety of lengths of handles is required, it is necessary either to have a number of flat finishing boxes, each attached to a specific length handle or to use fewer boxes than handle lengths required, (usually one box) and interchange the box or boxes from handle to handle in order to have the box on a handle of suitable length. The use of multiple boxes, each with a different length handle attached, is not generally acceptable because of the cost and because the compound used in the boxes sets up, i.e. hardens, so that compound in boxes not fully emptied in use is wasted and removal of the wasted compound is time consuming. The use of fewer boxes than handles is standard practice but changing the boxes from handle to handle is time consuming and tends to be awkward if the box contains the compound referred to in the trade as xe2x80x9cmudxe2x80x9d.
Therefore, for flat finishing drywall joints more efficiently in terms of the interrelated factors of time and cost, there has been a need for a flat finishing tool with an adjustable length handle, particularly one adjustable to specific lengths in a range of lengths.
U.S. Pat. No. 5,099,539 (Forrester) and U.S. Pat. No. 5,088,147 (MacMillan, the inventor of the subject invention) and U.S. patent application, Ser. No. 09/414,677, U.S. Pat. No. 6,260,238, also by MacMillan all show adjustable length handles for flat finishers. All of these handles have a lever pivoted at one end and a part called a box footplate pivoted at the other. In use a flat finishing box is attached to the footplate, the handle is adjusted to the needed length, and the handle is maneuvered to place the box against the work surface. This placement sets the box and footplate at an angle to the long axis of the handle and the lever is operated to lock the box and footplate at that angle relative to the handle. The mechanical complexity of these prior art adjustable length handles for flat finishers is typical in the prior art and increases first and maintenance costs of the handles and degrades their reliability, thereby increasing operation costs. The lock mechanism in particular tends to be delicate relative to its performance requirements and the range of angular motion of the box footplate is quite limited. The handle of U.S. patent application, Ser. No. 09/414,677, U.S. Pat. No. 6,260,238 is considered to be the least complicated and most rugged of the three prior art handles. Nevertheless, there is a continued need for more ruggedness. Also, there is a newly recognized need for two degrees of freedom of angular adjustment of the footplate (and attached box) relative to the handle.
Accordingly, the primary objective of the subject invention is to provide a less complicated adjustable length handle for flat finishers because of the significant savings in costs that the reduced complication facilitates. Other objectives are that the range of angular motion of the box footplate be relatively large, that there be two degrees of freedom of angular adjustment of the box footplate relative to the handle, that there be no highly loaded small parts, that the handle be relatively lightweight and that it be ergonomically acceptable.
The subject invention is an adjustable length handle for flat finishers. The primary structural components of the handle are two telescopic tubes. Relative rotation of the engaged tubes is prevented by engagement of a longitudinal rib on the outside of one tube with a groove in a fitting on the other tube. When the tubes are telescopically engaged each has an overlapped end and a free end. A fitting termed a box footplate is pivotally attached to the free end of the larger, outer tube, with two orthogonal pivot axes perpendicular to the long axis of the tubes. A first pivot of the box plate is a shaft running in bearings in a second fitting. A bevel gear on this pivot shaft for the box plate engages a second bevel gear which is mounted on a second shaft which extends through a fitting assembly which pivotally connects the second fitting and box plate to the free end of the larger tube. This second pivot connection provides a second degree of angular freedom of the box footplate relative to the axis of the handle. The axis of this second pivot connection is perpendicular to the axis of the pivot shaft for the box plate and to the axis of the handle. The fitting assembly is pivoted in a fixture assembly which is attached to the free end of the larger tube and includes a universal joint which connects the second shaft, through the fitting assembly, to a hex shaft assembly which is journalled in the larger tube with its axis coincident with the handle axis. The intersection of the axes of the universal point lies in the axis of the second pivot connection. The angular adjustment about the second pivot axis is manually made and locked in one of three positions. The primary component of the shaft assembly is a hexagonal rod which engages a hexagonal hole in a fitting attached to a torque assembly journalled in the smaller diameter tube and extending the full length of that tube. The hexagonal tube in the hexagonal hole causes the rotation of the torque tube to be the same as the rotation of the hex rod. As the larger and smaller handle tubes are telescopically adjusted to adjust handle length, the hex rod telescopes in the tube of the torque tube assembly.
A bushing, part of the torque tube assembly, is installed on the end of the torque tube in a rear fitting attached to the free end of the smaller tube. The bushing is engaged by a lever operated clamp, the clamp and lever being mounted in rear fitting. Operation of the lever engages the clamp on the bushing, preventing rotation of the torque tube assembly, the hex shaft assembly, the universal joint and thereby the angular movement of the box plate relative to the handle about the first pivot connection.